Forty-three patients subjected to thoracic, abdominal, or other operative procedures were studied to determine whether lung perfusion scintiscans had potential value for estimation of postoperative pulmonary function. Spirometry, alveolar-arterial oxygen difference, peak arterial oxygen tension, physiologic dead space, and scintiscans were done at regular intervals following operation for comparison with preoperative measurements. Mean values for pulmonary function showed maximal depression on the day of operation or within the first three postoperative days. Significant alterations in the postoperative scintiscans were observed in only 14 of the 43 patients, and the extent of scintiscan changes did not correlate with the degree of reduction in pulmonary function. More importantly, the scintiscans failed to reflect any change in distribution of pulmonary blood flow in the majority of patients who had equally significant reduction in pulmonary function.